Transformers worksheet with answers

Free printable Transformers worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

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1.Easy

An ideal transformer must step 800 V down to 400 V. Its primary winding has 200 turns. How many turns N₂ does the secondary winding need?

V₁ = 800 VV₂ = 400 VN₁ = 200

N₂ =

2.Easy

An ideal transformer has 250 turns on its primary winding and 6250 turns on its secondary winding. The primary is connected to a 400 V AC supply. Find the secondary voltage V₂.

N₁ = 250N₂ = 6250V₁ = 400 V

V₂ = V

3.Medium

An ideal transformer with a turns ratio N₁:N₂ = 10:1 has 2300 V applied to its primary winding. A 60 Ω resistor is connected across the secondary winding. Find the primary current I₁.

N₁:N₂ = 10:1V₁ = 2300 VR_L = 60 Ω

I₁ = A

4.Medium

A single-phase 150 kVA, 2400/240 V transformer operates at its rated load. Treat it as ideal. Find the current I_HV in the high-voltage winding.

S = 150 kVAV₁ = 2400 VV₂ = 240 V

I_HV = A

5.Hard

A single-phase 200 kVA transformer has a core loss of 800 W. At rated load and a power factor of 0.8 lagging its efficiency is 98.8%. Find the full-load copper loss P_cu,fl in watts.

S = 200 kVAP_core = 800 Wpf = 0.8η = 98.8%

P_cu,fl = W

6.Hard

A single-phase 75 kVA transformer has a core loss of 450 W and a copper loss of 1800 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 75 kVAP_core = 450 WP_cu,fl = 1800 W

S_η,max = kVA

Answer key

1. N₂ = 100
2. V₂ = 10000 V
3. I₁ = 0.3833 A
4. I_HV = 62.5 A
5. P_cu,fl = 1143 W
6. S_η,max = 37.5 kVA

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